Method and apparatus for managing route information and forwarding data in access  devices

ABSTRACT

The present invention provides a method for creating routes in access devices of the communication network by using access response messages. With the method provided by the present invention, services can be distinguished and forwarded based on destination IP sub-networks, so that different services can be distributed in access devices. In this way, on the premise that services are distinguished based on layer 3, the requirements for access devices are reduced and layer 2 networks on the user side are not required to carry out route protocols, which decreases administrators&#39; maintenance work and is the important condition for the realization of plug&amp;play and reduces the requirements for marginal routers.

TECHNICAL FIELD

The present invention relates to the communication network, particularlyto the access network of the communication network.

BACKGROUND OF THE INVENTION

Currently, the requirements for layer 2 access devices put forward bytelecom operators are higher and higher. Layer 2 devices are required todistinguish services based on layer 3 information, so that differentservices, such as audio, video, Internet and so on, can be distributedin access devices like the Digital Subscriber Line-Access Multiplexer(DSLAM) and access to corresponding service networks via gatewayscorresponding to different services. Concretely, operators willgenerally plan service networks in advance, and different serviceproviders possess different IP addresses. In this way, access devicescan distinguish and forward services based on destination IPsub-networks. However, common access devices are only layer 2 devicesand not used as user gateways, therefore these access devices aretransparent to users in the third layer. Moreover, they don't havededicated IP addresses for forwarding data. Therefore, accordingly, thenetwork can only create unnumbered IP interfaces to meet thisrequirement. And this is also used to cope with the requirement forsaving IPv4 addresses which are becoming scarcer.

Presently, there is a method for creating route tables by monitoringroute protocol messages. But operators normally don't enable routeprotocols on the ports on the user side. Route protocols based on linkstatuses (e.g. Open Shortest Path First) normally requires thecorrespondent node to have layer 3 addresses, however, this requirementcan not be satisfied. Although route protocols based on distance vectors(e.g. Routing Information Protocol) are usable, restrictions are putforward when operators choose route protocols, and employing routeprotocols in the user-end network increases the complexity of thenetwork and the load of the layer 2 network. Since layer 2 devicesshould support route protocols in this way, higher requirements are putforward for them.

Generally, it is very difficult for layer 2 devices to obtain layer 3route information. Configuring each such access device statically notonly leads to high work load, but also makes layer 2 devices lose theiradvantage of plug&play. Thus, this becomes a relative prominent problem.

The present invention proposes a method and an apparatus fordistinguishing services and forwarding data based on destination IPsub-networks by creating routes on layer 2 devices via the use of accessresponse messages generated by servers when terminal devices access tothe network. Here, the access response message refers to the DynamicHost Configuration Protocol (DHCP) response message. Below, a briefintroduction will be made about the DHCP.

Dynamic Host Configuration Protocol (DHCP):

The DHCP can be divided into two parts: one is the server end, while theother is the client end. DHCP servers run centralized management of allIP network setting information, and are responsible for dealing withDHCP requirements of the client end; while the client end uses IPenvironment information assigned from servers.

1. Assignment Forms of DHCP

At first, there must be at least one DHCP server working in the network.It monitors DHCP requirements of the network and negotiates with theclient end about the setting environment of TCP/IP. Two kinds of IPpositioning ways are provided:

automatic assignment, its circumstance is: once the DHCP client end hassuccessfully leased an IP address from the DHCP server for the firsttime, it will use this address for ever;

dynamic assignment: once the DHCP client end has leased an IP addressfrom the DHCP server for the first time, it doesn't use this address forever. As long as the lease expires, the client end should release thisIP address, so as to provide it to other work stations. Of course, theclient end can renew the lease with higher priorities than other hosts,or lease other IP addresses.

2. Work Principle of DHCP

Depending on whether it is the first time for the client end to log onthe network, the working form of DHCP will be different. Below, theworking form of DHCP when it is the first time for the client end to logon the network will be detailed described with reference to FIG. 1.

Logging on the network for the first time:

1) Searching Server. When the DHCP end client logs on the network forthe first time, namely the client finds there is no IP informationsetting in the host, it will send a DHCPDISCOVER packet to the network.Since the client hasn't known to which network it belongs yet, thesource address of the packet is 0.0.0.0, and the destination address is255.255.255.255, then the packet is attached with DHCPDISCOVERinformation and broadcasted to the network.

Under the circumstances of the Windows default setting, the waiting timeof DHCPDISCOVER is preset as 1 second, namely after the client end hassent the first DHCPDISCOVER packet, if no response is obtained within 1second, the second DHCPDISCOVER broadcast will be performed. Under thecircumstances that no response is obtained all along, the client endwill conduct totally four DHCPDISCOVER broadcasts (including the firstDHCPDISCOVER broadcast), the waiting time for the first broadcast is 1second, and the waiting time for the other three broadcasts is 9seconds, 13 seconds and 16 seconds respectively. If there is still noresponse of the DHCP server, the client end will display errorinformation and declares the failure of DHCPDISCOVER. After that, basedon the choice of the user, the system will continue to repeat theDHCPDISCOVER process once again after 5 minutes.

2) Providing an IP lease address. After the DHCP server has monitoredthe DHCPDISCOVER broadcast sent by the client end, it will choose themost front unleased IP address from the range of the addresses whichhave not been leased, together with other TCP/IP settings, to form aDHCPDISCOVER packet and sent the same to the client end as a response.

Since the client end doesn't have IP address at the beginning, there isMAC address information contained in the DHCPDISCOVER packet, and thereis an XID number to identify this packet. Based on this information, theDHCPOFFER packet responded by the DHCP server is forwarded to the clientneeding the lease. According to the setting of the server end, theDHCPOFFER packet contains information of the lease term.

3) Accepting an IP lease. If the client end receives responses ofmultiple DHCP servers in the network, it will only choose one of theDHCPOFFERs (generally the one that arrives earliest), and send aDHCPREQUEST broadcast packet to the network in order to tell all DHCPservers that it will accept the IP address provided by which server.

At the same time, the client end will also send an ARP packet to thenetwork to enquire whether there are any other hosts using this IPaddress in the network; if it is found that this IP address has beenoccupied, the client end will send a DHCPDECLINE packet to the DHCPserver, so as to decline to accept its DHCPOFFER and resend aDHCPDISCOVER message.

4) Acknowledging the lease. After the DHCP server has received theDHCPREQUEST of the client end, it will send a DHCPACK response to theclient end in order to acknowledge that the IP lease has come intoeffect formally, namely a whole DHCP working process is completed.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method, in accessdevices of the communication network, for making use of access responsemessages to create routes, so as to distinguish services and forwardbased on destination IP sub-networks and make different servicesdistribute in access devices.

According to the first aspect of the present invention, there isprovided a method for managing route information in an access device ofthe communication network. The method comprises the steps of: at first,receiving an access response message which is from the server and sentto a user terminal; then, extracting route-related information from saidaccess response message, and creating or updating the route table basedon said route-related information.

According to the second aspect of the present invention, there isprovided a route management apparatus for managing route information inan access device of the communication network. The route managementapparatus comprises a receiving means, a first obtaining means and aroute maintenance means. The receiving means receives an access responsemessage which is from the server and sent to a user terminal; the firstobtaining means extracts route-related information from said accessresponse information; the route maintenance means creates or updates theroute table based on said route-related information.

According to the third aspect of the present invention, there isprovided a method for forwarding data in an access device of thecommunication network, wherein data from user terminals belonging todifferent sub-networks is forwarded to corresponding sub-networkgateways.

According to the fourth aspect of the present invention, there isprovided a forwarding apparatus for forwarding data in an access deviceof the communication network, wherein data from user terminals belongingto different sub-networks is forwarded to corresponding sub networkgateways.

As compared with the prior art, the present invention has followingadvantages:

1. Not influencing the choice of route protocols;

2. Not requiring layer 2 network on the user side to execute routeprotocols;

3. Reducing the requirements for the marginal routers;

4. Reducing the maintenance work of administrators, which is theimportant condition for realizing plug&play;

5. Under the premise that services are distinguished based on layer 3,reducing the requirements for access devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention will beapparent by reading the following detailed description of non-limitingexemplary embodiments with reference to appended drawings.

FIG. 1 a illustrates the frame structure of DHCP;

FIG. 1 b illustrates the option structure in the frame structure ofDHCP;

FIG. 2 illustrates the flowchart of the method for managing routeinformation in an access device of the communication network accordingto an embodiment of the present invention;

FIG. 3 a illustrates a network topological structure of the accessnetwork according to an embodiment of the present invention;

FIG. 3 b illustrates another network topological structure of the accessnetwork according to an embodiment of the present invention;

FIG. 4 illustrates the block diagram of the route management apparatusfor managing route information in an access device of the communicationnetwork according to an embodiment of the present invention;

FIG. 5 illustrates the flowchart of the method for forwarding data in anaccess device of the communication network according to an embodiment ofthe present invention;

FIG. 6 illustrates the block diagram of the forwarding apparatus forforwarding data in an access device of the communication networkaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 a illustrates the encapsulation format of a DHCP packet. All DHCPmessages are encapsulated in UDP packets. The options in DHCP arevendor-specific area, so as to provide more setting information (e.g.Netmask, Gateway, DNS, etc.), and its length can be variable and therecan be multiple options at the same time. The first byte of each optionis the option code, its subsequent byte shows the length of the optioncontent hereafter, and the rest is the option content, such as theoption format in a DHCP message shown in FIG. 1 b. DHCP employs theoption code 0x53 to set the packet type: 1 represents DHCP-DISCOVER, 2represents DHCP-OFFER, 3 represents DHCP-REQUEST, 4 representsDHCP-DECLINE, 5 represents DHCP-ACK, 6 represents DHCP-NACK and 7represents DHCP-RELEASE.

In the DHCP standard, three static route-related options are defined:option 3, option 33 and option 121. Wherein, option 3 is used to declarethe gateway corresponding to the client. There can be multiple gatewaysin correspondence with the client, which are ordered according to thepriority. Option 33 is put forward relative early, and is used todeclare static type route information. Option 121 comprises the formertwo. It declares all static routes, including default routes, andsupports Classless Inter-Domain Routing. These options are configured tothe client end at the same time when the server is assigning IPaddresses, so that the client end can create the route table correctly.It is worth noting that, for the whole network, user gateways and planedaddresses of service providers are not often changed. They are locatedat two ends of the IP addresses and are the end points of the networktopology and won't change with the network topology. Therefore, theseroutes can be regarded as static and can be pre-configured in the serverby administrators. The configuration load is also not very large.

For an access device, it is located between the marginal router and theuser and won't be influenced by the topology change. Hence, these staticroutes are sufficient for the access device.

Considering the current situation of the network, Classless Inter-DomainRouting has been widely used. An access device should learn and maintainthe upstream route mainly depending on monitoring option 121 in eachDHCP-ACK packet.

Below, the present invention will be further elucidated in conjunctionwith FIG. 2 to FIG. 6.

FIG. 2 illustrates the flowchart of the method for managing routeinformation in an access device of the communication network accordingto an embodiment of the present invention.

At first, in step S11, an access response message which is from a serverand sent to a user terminal is received.

Then, in step S12, route-related information is extracted from saidroute-related message.

Finally, a route table item is created or updated based on saidroute-related information.

If said access response message further comprises the predefined usingtime indicating the time which can be used by said route, then in stepS12, said predefined using time is obtained simultaneously; finally, theroute table item is updated or created in conjunction with saidroute-related information and said predefined using time.

Wherein the step in which said route table item is updated or createdcan be concretely divided into steps S13, S14, S15 and S16.

At first, in step S13, judging whether a route table item correspondingto said route-related information exists in said route table.

If a route table item corresponding to said route-related informationexists in said route table, then in step S14, judging whether theremaining time of said route table item is shorter than said predefinedusing time.

If the remaining time of said route table item is shorter than saidpredefined using time, then updating the remaining time of said routeitem to the said predefined using time.

If no route table item corresponding to said route-related informationexists in said route table, then in step S16, creating a route-relateditem corresponding to said route-related information.

If the virtual local area network (VLAN) configuration is employedbetween an access device and each sub-network gateway (also referred toas a marginal router) connected with the access device, correlatedinformation of said route table item and the VLAN is obtained from theaddress resolution protocol (ARP) message or the access responsemessage.

FIGS. 3 a and 3 b illustrates two network topological structures of theaccess network according to an embodiment of the present invention. InFIG. 3 a, each VLAN has a server responding to user access requests. InFIG. 3 b, three VLANs share a server responding to user access requests.

In general cases, such as the network topological structure graphs shownin FIGS. 3 a and 3 b, the access device 0 can obtain information of theVLAN via the VLAN tag in the acknowledgment frame of the ARP from eachsub-network gateway, and correlate the information with correspondingroute. The detailed flow is as below: at first, the access device 0receives a packet from a user device. Assume that the packet is sent tothe service a (world wide web). Based on the source network address andthe destination network address in the packet, the access device 0 findsthe destination network address of the next hop of the forwarding, thensends a ARP request frame to the host of the next hop (namely themarginal route a shown in FIGS. 3 a and 3 b) so as to inquire its linklayer address. After receiving this request, the host of the next hopresponds with an ARP response frame comprising a VLAN tag. Whenreceiving said ARP response frame comprising a VLAN tag, the accessdevice 0 extracts the information of the VLAN and correlates it with theroute.

If there is one (or more) server(s) in each VLAN which responds to useraccess requests, as shown in FIG. 3 a, under such network configuration,information of the VLAN can also be obtained by the VLAN tag in anaccess response message, and then correlated with the route-relatedinformation. If multiple VLANs share one server responding to useraccess requests, as shown in FIG. 3 b, then the VLAN informationcorrelated with the route-related information can not be obtained viathe VLAN tag in the access response message. At this time, the VLANinformation correlated with the route-related information can only beobtained by the ARP message.

In current network realizations, aforesaid access request message andaccess response message are DHCP messages, and said predefined usingtime is the lease time in the DHCP message.

FIG. 4 illustrates the block diagram of the route management apparatus 1for managing route information in an access device of the communicationnetwork according to an embodiment of the present invention. The routemanagement apparatus 1 comprises a receiving means 11, a first obtainingmeans 12, a second obtaining means 13 and a route maintenance means 14.Wherein the route maintenance means 14 comprises a first judging means141, a second judging means 142, an updating means 143 and a creatingmeans 144.

At first, the receiving means 11 receives an access response messagewhich is from the server end and sent to the terminal.

Then, the first obtaining means 12 obtains said route-relatedinformation from said access response message and obtains a predefinedusing time at the same time. The predefined using time is used toindicate the using time of said route.

If the VLAN configuration is employed between an access device and eachsub-network gateway (also referred to as a marginal router) connectedwith the access device, the second obtaining means 13 obtains thecorrelated information of said route table item and the VLAN from theARP message or the access response message.

In general cases, as shown in FIGS. 3 a and 3 b, the information of theVLAN can be obtained via the VLAN tag in the acknowledgment frame of theARP from each sub-network gateway, and correlate the information withcorresponding route. The detailed flow is as below: at first, the accessdevice 0 receives a packet from a user device. Assume that the packet issent to the service a (world wide web). Based on the source networkaddress and the destination network address in the packet, the accessdevice 0 finds the destination network address of the next hop of theforwarding, then sends a ARP request frame to the host of the next hop(namely the marginal route a shown in FIGS. 3 a and 3 b) so as toinquire its link layer address. After receiving this request, the hostof the next hop responds with an ARP response frame comprising a VLANtag. When receiving said ARP response frame comprising a VLAN tag, theaccess device 0 extracts the information of the VLAN and correlates itwith the route.

If there is one (or more) server(s) in each VLAN which responds to useraccess requests, as shown in FIG. 3 a, under such network configuration,information of the VLAN can also be obtained by the VLAN tag in theaccess response message, and then correlated with the route-relatedinformation. If multiple VLANs share one server responding to useraccess requests, as shown in FIG. 3 b, then the VLAN informationcorrelated with the route-related information can not be obtained viathe VLAN tag in the access response message. At this time, the VLANinformation correlated with the route-related information can only beobtained by the ARP message.

Finally, the route maintenance means 14 creates or updates the routetable based on said route-related information.

In a preferred embodiment of the route maintenance means 14, accordingto the route-related information, the predefined using time obtained bythe first obtaining means 12 and the VLAN information obtained by thesecond obtaining means 13, the first judging means 141 first judgeswhether a route table item corresponding to said route-relatedinformation exists in said route table.

If a route table item corresponding to said route-related informationexists in said route table, the second judging means 142 judges whetherthe remaining time in said route table item is shorter than saidpredefined using time.

If a route table item corresponding to said route-related informationexists in said route table and the remaining time in said route tableitem is shorter than said predefined using time, the updating means 143updates the remaining time of said route table item to the predefinedusing time.

If no route table item corresponding to said route-related informationexists in said route table, the creating means 144 creates a route tableitem corresponding to said route-related information.

In current network realizations, aforesaid access request message andaccess response message are DHCP messages, and said predefined usingtime is the lease time in the DHCP message.

FIG. 5 illustrates the flowchart of the method for forwarding data in anaccess device of the communication network according to an embodiment ofthe present invention. The method consists in that data from userterminals belonging to different sub-networks is forwarded tocorresponding sub-network gateway. As shown in FIG. 5, the method can bedivided into four steps.

At first, in step S21, a packet from a user terminal is received.

Then, in step S22, the source network address and the destinationnetwork address are obtained from the packet.

After that, in step S23, based on the source network address and thedestination network address of said packet, a gateway which can get tothe destination network and matches the source network address isinquired from the route table. In addition, the forwarding portcorresponding to said gateway is also obtained.

Finally, in step S24, the packet is sent to the gateway of saidcorresponding sub-network via said forwarding port.

In current network realizations, aforesaid network addresses are IPaddresses.

In a preferred embodiment, an access device maintains a sub-networkroute table respectively for each sub-network. At first, a packet from auser terminal is received; then, based on the source IP address of saidpacket, a corresponding sub-network route table is inquired; after that,based on the destination IP address of said packet, the correspondingroute table item is inquired from said corresponding sub-network routetable, so as to determine the forwarding port of said packet; finally,the packet is sent to the gateway of said corresponding sub-network viasaid forwarding port.

In another preferred embodiment, an access device only maintains oneroute table. At first, a packet coming from a user terminal is received;then based on the destination IP address of said packet, one or moreroute table items correlated with said destination address are inquiredfrom said route table; after that, by using the source IP address ofsaid packet, the route table item corresponding to the gateway belongingto its sub-network is determined from said one or more route table itemscorrelated with said destination address, and the forwarding port ofsaid packet is also determined; finally, the packet is sent to saidcorresponding sub-network's gateway via said forwarding port.

FIG. 6 illustrates the block diagram of the forwarding apparatus 2 forforwarding data in an access device of the communication networkaccording to an embodiment of the invention. The forwarding apparatus 2forwards data from user terminals of different sub-networks to thegateways of corresponding sub-networks.

The forwarding apparatus comprises a receiving means 21, an obtainingmeans 22, an inquiring means 23 and a sending means 24.

At first, the receiving means 21 receives a packet from a user terminal.

Then, the obtaining means 22 obtains the source network address and thedestination network address from said packet.

After that, based on the source network address and the destinationnetwork address of said packet, the inquiring means 23 inquires agateway from the route table which can get to the destination networkand match the source network address, and a forwarding portcorresponding to said gateway.

Finally, the sending means 24 sends said packet to the gateway of saidcorresponding sub-network via said forwarding port.

In current network realizations, aforesaid network addresses are IPaddresses.

In a preferred embodiment, an access device maintains a sub-networkroute table respectively for each sub-network. At first, the receivingmeans 21 receives a packet from a user terminal; then, the obtainingmeans 22 obtains the source network address and the destination networkaddress from said packet; after that, based on the destination IPaddress of said packet, the inquiring means 23 inquires itscorresponding sub-network route table; and then, based on thedestination IP address of said packet, the inquiring means 23 inquiresthe corresponding route table item from said corresponding sub-networkroute table, so as to determine the forwarding port of said packet;finally, the sending means 24 sends said packet to the gateway of saidcorresponding sub-network via said forwarding port.

In another preferred embodiment, an access device only maintains oneroute table. At first, the receiving means 21 receives a packet comingfrom a user terminal; then, the obtaining means 22 obtains the sourcenetwork address and the destination network address from said packet;after that, based on the destination IP address of said packet, theinquiring means 23 inquires one or more route table items correlatedwith said destination address from said route table; afterwards, byusing the source IP address of said packet, the route table itemcorresponding to the gateway belonging to its sub-network is determinedfrom said one or more route table items correlated with said destinationaddress, and the forwarding port of said packet is also determined;finally, the sending means sends said packet to the gateway saidcorresponding sub-network via said forwarding port.

Above, embodiments of the present invention have been described. Itshould be understood that the present invention is not limited toaforementioned specific embodiments. Those skilled in the art can makevarious variations and modifications within the scope of the appendedclaims.

1. A method, in an access device of the communication network, formanaging route information, comprising: a. receiving an access responsemessage which is from a server and sent to a user terminal; b. obtainingroute-related information from said access response message; c. based onsaid route-related information, creating or updating a route table item.2. A method according to claim 1, wherein said step b further comprises:obtaining a predefined using time from said access response message,said predefined using time indicates a using time of said route; whereinsaid step c further comprises: based on said predefined using time,updating said route table item.
 3. A method according to claim 2,wherein said step of updating said route table item based on saidpredefined using time further comprises: judging whether a route tableitem corresponding to said route-related information exists in saidroute table; if a route table item corresponding to said route-relatedinformation exists in said route table and the remaining time of saidroute table item is shorter than said predefined using time, thenupdating the remaining time of said route table item to said predefinedusing time; if a route table item corresponding to said route-relatedinformation doesn't exist in said route table, then creating a routetable item corresponding to said route-related information.
 4. A methodaccording to claim 1, further comprising steps of: obtaining correlatedinformation of said route table item and a virtual local area networkfrom an address resolution protocol message or an access responsemessage; wherein said virtual local area network configuration isemployed between said access device and each marginal router connectedwith said access device.
 5. A method according to claim 1, wherein saidaccess response message refers to a dynamic host configuration protocolresponse message, said predefined using time refers to the lease time insaid dynamic host configuration protocol response message.
 6. A routemanagement apparatus, in an access device of the communication network,for managing route information, comprising: a receiving means,configured to receive an access response message which is from a serverand sent to a terminal; a first obtaining means, configured to obtainsaid route-related information from said access response message; aroute maintenance means, configured to create or update a route tablebased on said route-related information.
 7. An apparatus according toclaim 6, wherein said obtaining means is further configured to obtain apredefined using time from said access response message, said predefinedusing time is used to indicate the using time of said router; wherein,said route maintenance means updates said route table item further basedon said predefined using time.
 8. An apparatus according to claim 6,wherein said route maintenance means comprises: a first judging means,configured to judge whether a route table item corresponding to saidroute-related information exists in said route table; a second judgingmeans, configured to judge whether the remaining time of said routetable item is shorter than said predefined using time when a route tableitem corresponding to said route-related information exists in saidroute table; a updating means, configured to update the remaining timeof said route table item to said predefined using time when a routetable item corresponding to said route-related information exists insaid route table and the remaining time of said route table item isshorter than said predefined using time; a creating means, configured tocreate a route table item corresponding to said route-relatedinformation when no route table item corresponding to said route-relatedinformation exists in said route table.
 9. An apparatus according toclaim 6, further comprising: a second obtaining means, configured toobtain correlated information of said route table item and a virtuallocal area network; wherein, said virtual local area networkconfiguration is employed between said access device and each marginalrouters connected with said access device.
 10. An apparatus according toclaim 6, wherein said access response message refers to a dynamic hostconfiguration protocol, said predefined using time refers to the leasetime in said dynamic host configuration protocol response message.
 11. Amethod, in an access device of the communication network, for forwardingdata, wherein data coming from user terminals of different sub-networksis forwarded to corresponding sub-network gateway.
 12. A methodaccording to claim 11, comprising steps of: a. receiving a packet from auser terminal; b. obtaining the source network address of thedestination network address from said packet; c. based on said sourcenetwork address and destination network address, inquiring a gatewaywhich can get to the destination network and matches the source networkaddress from a route table, and a forwarding port corresponding to saidgateway; d. sending said packet to the gateway of said correspondingsub-network via said forwarding port.
 13. A forwarding apparatus, in anaccess device of the communication network, for forwarding data, whereindata coming from user terminals of different sub-networks is forwardedto gateways of corresponding sub-networks.
 14. An apparatus according toclaim 13, comprising: a receiving means, configured to receive a packetfrom a user terminal; an obtaining means, configured to obtain thesource network address and the destination network address from saidpacket; an inquiring means, configured to inquire a gateway which canget to the destination network and matches the source network addressfrom a route table, and a forwarding port corresponding to said gateway;a sending means, configured to send said packet to the gateway of saidcorresponding sub-network via said forwarding port.
 15. An access devicein the communication network, wherein said access device comprises aroute management apparatus according to claim
 6. 16. A device accordingto claim 15, wherein said access device is a digital subscriberline-access multiplexer.
 17. An access device in the communicationnetwork, wherein said access device comprises a forwarding apparatusaccording to claim 13.